This invention generally relates to apparatus for modifying foamed plastic masses and, more particularly, to an apparatus for applying modifying ingredients to a mass of open celled polyurethane foam such as foam sheets.
Early methods for applying dyes, pigments and other modifying ingredients to open-celled polyurethane foam and other open-celled foams were based generally upon adhesion of the modifying ingredient to the surface of the foam, as by painting, or upon physical mixing of the modifying ingredient with the constituents prior the foam formation.
An improved method of applying modifying ingredients to open-celled polyurethane material is disclosed in my U.S. Pat. No. Re. 31,844 dated Mar. 5, 1985 (Reissue of U.S. Pat. No. 4,073,979 dated Feb. 14, 1978) which is assigned to the asignee of the present invention. In that improved method, the application of a modifying ingredient, such as a dye, pigment, color stabilizer or fire retardant, for example, contemplates applying an excess of a liquid solution or dispersion of the modifying ingredient to a mass of the foam, such as a foam sheet. A continuous strip of the sheet runs between opposed rollers in a tank of the liquid solution or dispersion whereat inhaling action takes place below the surface of the liquid so that there is little oppurtunity for the inhalation of air rather than the liquid. The continuous sheet then is fed through a set of squeeze rollers placed immediately after the dispersion dye tank where the sheet passes through a pressure nip between the rollers, the nip being tight enough to return most of the excess moisture to the liquid solution or dispersion tank. The pickup of shade from the dye is a function of the degree of squeeze between the rollers. Thereafter, the sheet is passed through a heating station which creates a suction to pass through gaseous material entirely through the mass containing the remainder of the liquid solution or dispersion to rapidly raise the temperature of the entire mass or sheet. The temperature is at least as high as the vaporization temperature of the liquid under the ambient condition of operation, and the period of exposure of the mass to the gaseous material is such that the liquid is vaporized and the modifying ingredient is effectively, simultaneously incorporated into the foam in a very short time.
The improved method described above has proven effective for modifying foam masses with various ingredients such as dyes, pigments, color stabilizers and fire retardants, including masses or sheets having a thickness greater than about 3/32 inch.
In such applications, the pressure applied by the rollers in the liquid solution or dispersion tank, some of which are driven, is not necessarily critical. On the other hand, it has been found that the prior art methods of applying modifying ingredients to such masses of open-celled polyurethane foam are ineffective when dealing with certain other modifying ingredients. For instance, if it is desirable to apply a modifying ingredient such as a highly soluble salt to a mass of open-celled polyurethane foam, extraordinary pressures are required while the mass or sheet is passed through the liquid solution or dispersion tank in order to pickup substantially all of the salt in the liquid solution. The problem is magnified when it is necessary to obtain uniform pickup either across the mass or continuous sheet or along the sheet. Conventional or previously known roller assemblies have proved inadequate for use with modifying ingredients such as soluble acid dyes or highly soluble salt, because they either are incapable of applying the large pressures necessary in the solution or dispersion tank or they do not apply sufficiently uniform pressures to obtain a uniform modification of the foam. In fact, it has been discovered that the amount of pickup of such modifying ingredients, such as highly soluble salts or acid dyes, is a function of the pressure applied to the mass in the liquid solution or dispersion tank.
This invention is directed to providing a new and improved apparatus for applying a modifying ingredient to a mass of open-celled polyurethane foam where high pressures are required for effective and uniform pickup of the modifying ingredient.